Conventionally, a III-nitride semiconductors made of compounds in which N is combined with Al, Ga, In, etc. are used as materials for ultraviolet light-emitting devices. In particular, III-nitride semiconductors made of high-Al-composition AlGaN are used for ultraviolet light-emitting devices or deep ultraviolet light-emitting devices (DUV-LEDs) emitting light at a wavelength of 300 nm or less.
Examples of the characteristics required of III-nitride semiconductor light-emitting devices include, but not limited to, high external quantum efficiency properties and low resistance properties. The applicant of the present application has previously proposed in JP 2010-161311 A (PTL 1) that the light emission efficiency can be improved by forming a layer serving as an energy barrier for electrons, which is called an electron blocking layer, between a light emitting layer having a quantum well structure and a p-type cladding layer. The electron blocking layer serves as a barrier against a quantum well layer of the light emitting layer and prevents electrons from flowing excessively, thereby improving carrier injection efficiency.
JP 2009-152491 A (PTL 2) discloses a nitride semiconductor device in which a mixed doped GaN layer with a film thickness of 25 nm or less, obtained through co-doping with a p-type impurity and an n-type impurity to a p-type impurity concentration of 1×1019 atoms/cm3 or more and an n-type impurity concentration of 1×1019 atoms/cm3 or more, is provided on a p-type GaN layer, and an electrode is formed on the mixed doped GaN layer. According to PTL 2, the mixed doped GaN layer reduces contact resistance between the p-type GaN layer and the electrode, which allows a current to easily flow into the p-type GaN layer.